Variable inductance device

ABSTRACT

In an electronic fuel injection system, a transducer for converting a variable pressure signal to a variable inductance comprises an inductive coil surrounding an axially reciprocable, magnetically permeable plunger. Two opposing sides of one end of the plunger are asymmetrically tapered; and a magnetically permeable flux member attached to the coil has portions adjacent the untapered end of the plunger and both sides of the tapered end of the plunger to create parallel flux paths through the plunger, each of which has a gap defined by one of the tapered sides and has a reluctance which varies with axial movement of the plunger. The portion of the flux member adjacent one side of the tapered end is transversely movable with respect to the plunger by a torque arm and adjusting screw so as to vary the slope of the inductance-plunger position curve.

United States Patent [191 Hendrickson [451 Aug. 28, 1973 VARIABLEINDUCTANCE DEVICE [73] Assignee: General Motors Corporation,

Detroit, Mich.

[221 Filed: Dec. 15, 1972 [21] Appl. No.: 315,342

[56] References Cited UNITED STATES PATENTS 9/1955 Hale et a1. 336/13412/1966 Lyman..... 336/136 X 2,427,872 9/1947 Newman 336/136 X 2,513,1606/1950 Friend 336/133 X 1,720,446 7/1929 Sarazin 336/134 X PrimaryExaminer-Thomas J. Kozma Attorney-Paul Fitzpatrick et a1.

[5 7 ABSTRACT In an electronic fuel injection system, a transducer forconverting a variable pressure signal to a variable inductance comprisesan inductive coil surrounding an axially reciprocable, magneticallypermeable plunger. Two opposing sides of one end of the plunger areasymmetrically tapered; and a magnetically permeable flux memberattached to the coil has portions adjacent the untapered end of theplunger and both sides of the tapered end of the plunger to createparallel flux paths through the plunger, each of which has a gap definedby one of the tapered sides and has a reluctance which varies with axialmovement of the plunger. The portion of the flux member adjacent oneside of the tapered end is transversely movable with respect to theplunger by a torque arm and adjusting screw so as to vary the slope ofthe inductance-plunger position curve.

4 Claims, 5 Drawing Figures PATENIEMunza ma ll J INDUCTANCE MANIFOLDABSOLUTE PRESSURE INDUCTANCE MANIFOLD ABSOLUTE PRESSURE a ll VARIABLEINDUCTANCE DEVICE BACKGROUND OF THE INVENTION Many electronic fuelinjection systems for engines employ a pressure-inductance transducer inan electronic circuit to vary the duty cycle of a solenoid controlledfuel nozzle in accordance with the pressure in the engine air intakemanifold. Such a transducer generally comprises an evacuated bellows ina chamber open to the variable pressure, one end of the evacuatedbellows being fixed in the chamber and the other end being adapted toactuate a variable inductance device. The variable inductance devicegenerally comprises a magnetically permeable plunger reciprocable withina coil and mechanically connected to the moving end of the evacuatedbellows for co-movement therewith. A magnetically permeable flux member,fixed with respect to the coil, has one portion adjacent one end of theplunger and another portion adjacent the other end of the plunger toform, with the plunger, a magnetic flux path for the coil. One end ofthe plunger is tapered so that axial movement of the plunger varies thegap between the plunger and flux member; this varies the reluctance ofthe flux path and thus also the inductance of the device. The parametersof such a transducer are chosen to produce, in conjunction with the restof the system, a particular desired curve of fuel flow as a function ofmanifold absolute pressure.

An inherent problem of such a transducer, however, is that very closetolerances have to be met on a number of these parameters in order tokeep the desired curve within its tolerance limits. Although an axialadjustment for the fixed end of the evacuated bellows has been shown tobe an effective method of adjusting the transducer to match one point onthe desired curve, the remaining points on the desired and actual curvemay not coincide, since the slopes of the curves may differ. It would bedesirable to provide the capability of adjusting the slope of the curveso that expensive close tolerances would no longer have to be met.

An additional feature of most pressure-inductance transducers forelectronic fuel injection systems is a power enrichment boost in fuelflow at high manifold absolute pressures. Provision for this featurepresently requires additional mechanical devices within the transducer,such as an extra diaphragm with associated spring and stops. A typicaldesign for such a transducer is shown in US. application, Ser. No.202,760, filed Nov. 29, 1971, of common ownership with this application.

SUMMARY OF THE INVENTION This invention relates to a new and improvedvariable inductance device that can be used in an otherwise conventionalpressure-inductance transducer within a electronic fuel injectionsystem. The device incorporates features to provide adjustment of theslope of the inductance-manifold absolute pressure curve as well as thelateral translation of the curve and a power enrichment modification ofthe curve at high manifold absolute pressures.

: The device generally comprises a plunger axially reciprocable within aspool around which is wound an inductive coil. One end of the plunger isasymmetrically tapered on opposing sides thereof. A magneticallypermeable flux member fixed to the spool has portions passing adjacentthe ends of the plunger to provide two parallel flux paths, each ofwhich has an air gap variable by one of the tapered surfaces as theplunger moves axially within the coil. The tapered surfaces of theplunger are designed with such slope and length that one predominates atlow manifold absolute pressures and the other predominates at highmanifold absolute pressures. A torque arm projecting from the fluxmember is effective to deform the flux member so that the portionthereof which forms an air gap with the tapered side of the plungerpredominating at low manifold absolute pressure is moved transverselyaway from the plunger to vary the slope of the curve. An adjusting screwthreadably mounted in the spool has an end which engages the torque armto accomplish this result. Further objects and details of the inventionwill be apparent in the following drawings and description.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a typical electronic fuelinjection system for an engine.

FIG. 2 is a partial cutaway view of a variable inductance device for usein the system of FIG. 1.

FIG. 3 is a view along line 3-3 of FIG. 2.

FIG. 4 is a graph showing typical inductance-pressure curves for thesystem of FIG. 1.

FIG. 5 is a graph showing typical inductance-pressure curves for thesystem of FIG. I with power enrichment at high pressures.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, aninduction passage or manifold 2 has a throttle 4 which controls air flowto the engine. An injector nozzle 6 is disposed to discharge the fuelinto induction passage 2 adjacent the inlet valve 8 for the enginecombustion chamber. A separate nozzle 6 would ordinarily be provided foreach combustion chamber.

A housing 10 defines a transducer chamber 11, which is connected througha conduit 12 to the induction passage 2 downstream from the throttle 4;so that the induction passage pressure downstream from the throttle 4,hereinafter referred to as monifold absolute pressure, is communicatedto the transducer chamber 11. Within the transducer chamber 11, anevacuated bellows 14 has one axial end thereof fixed to an axiallyadjustable member 16 which comprises, for example, an adjusting screwthreadably mounted in the housing 10. The other axial end of theevacuated bellows 14, which moves axially in response to the changingmanifold absolute pressure, is mechanically linked to the movable member17 of a variable inductance device 18 to vary the inductance of thelatter in accordance with the aforementioned pressure.

The variable inductance device 18 also contains an inductive coil 19which is connected in an electronic circuit to control the operation ofthe injector nozzle 6. The circuit includes a pulse generator 20 whichapplies a negative pulse to a line 22 each time the injector nozzle 6 isto be actuated to inject fuel into the associated combustion chamber.The negative pulse renders an output transistor 24 nonconductive. Withthe output transistor 24 ofi, current flows through a solenoid winding26 to actuate nozzle 6 and initiate fuel injection. Nozzle 6 remainsactuated for a period of time determined by the remainder of theelectronic circuit.

The negative pulse also renders a control transistor 28 nonconductive.With control transistor 28 off, the voltage at a junction 30 betweenresistors 31 and 32 increases and renders a transistor 34 conductive anda transistor 36 nonconductive. With transistor 36 off, transistors 38and 40 are also rendered nonconductive. As long as transistor 40 is off,output transistor 24 remains off and permits current flow throughsolenoid 26 to actuate the injection nozzle 6.

The aforementioned transistors are maintained in the indicated state fora period of time determined by the L/R time constant provided by theinductance of the transducer coil 19 and the combined resistance of theresistors 31 and 32. When the time constant permits decay of the voltageat junction 30 to a predetermined level, transistor 34 is renderednonconductive and transistor 36 is thereby rendered conductive. Withtransistor 36 on, transistors 38 and 40 are rendered conductive. Astransistor 40 becomes conductive output transistor 24 becomesconductive, shorting out the solenoid 26 to de-energize the nozzle 6 andterminate fuel injection.

Thus the duration of fuel injection is controlled by the level of avoltage signal at junction 30 which in turn is controlled by an L/R timeconstant. In the simplified electronic control circuit shown here forpurposes of illustration, this time constant is varied solely by varyingthe inductance of the transducer coil 19. This inductance is varied inthe variable inductance device of this invention in a certain specifiedmanner by the manifold absolute pressure.

Referring to FIG. 2, the variable inductance device 18 is seen tocomprise a spool 50, made from a nonmagnetically permeable material,around which is wound the coil 19. The spool 50 has an axial hole 51, inwhich is disposed a plastic plunger guide 52. A movable member 17, whichcomprises a magnetically permeable plunger, is axially reciprocable withthe plunger guide 52, which may be lined with a low friction substanceto facilitate the reciprocation. As shown in FIG. 3, the plunger 17 andplunger guide 52 are rectangular in cross section, although many othershapes could be chosen. A magnetically permeable flux member 54 extendsaround the coil 19 and spool 50, as shown in FIGS. 2 and 3. The fluxmember 54 widens at one end, and this wider portion has an opening 56,through which the plunger guide 52 and plunger 17 extend. At the otheraxial end of the spool, two ends of the flux member 54, not joined,extend to the plunger guide 52. The flux member 54 and plunger 17 thusform two parallel flux paths for the coil 19, the common leg of which isthe plunger 17. These flux paths circle the coil through the flux member54 on opposite sides of the plunger 17. The end of the plunger 17 whichprojects through the opening 56 is axially constant in cross sectionalshape and area; and, therefore, the gap between the flux member 54 andthis end of the plunger 17 remains constant with axial movement of theplunger 17. The other end of the plunger 17, however, is tapered on thesides adjacent the two ends of the flux member 54; and these taperedsides produce a variation in the reluctance of the total magnetic fluxpath as the plunger 17 is moved axially within the spool. The twotapered sides have tapers of different length and depth; one side has ataper both shorter and shallower than the other.

' Flux member 54 has projecting from one side thereof and extendingcircumferentially part way around the coil 19, a torque arm 58. Anadjusting screw 60 is threadably mounted in the spool 50 near thenontapered end of the plunger 17x The adjusting screw 60 extends axiallytoward the tapered end of the plunger 17 and engages the free end of thetorque arm 58.

Prior art variable inductance devices of the moving plunger type haveneither the asymmetrical taper nor the torque arm, so far as I am aware.Typical curves of inductance versus manifold absolute pressure for atypical prior art variable inductance transducer are shown as A and B onthe graph of FIG. 4. Although curves A and B are similar in generalshape, they do not correspond exactly because of differences in variousparameters of the variable inductance device. If curve A describes thedesired characteristic but the assembled device produces curve B, anaxial adjustment for the movable plunger, such as that provided by theaxially adjustable member 16, permits the point C where curves A and Bintersect to be shifted anywhere along curve A. However, since theslopes of the curves are not changed they will intersect in only onepoint regardless of where that point is shifted.

In this invention, however, the slope of the inductance-pressurve curvecan be changed by the adjusting screw 60. As 17. can be seen in FIG. 2,the side of the plunger 17 having the shortest and shallowest taper isadjacent the side of the flux member 54 from which projects the torquearm 58. As the adjusting screw 60, in contact with the torque arm 58, ismoved toward the tapered end of the plunger 17, the torque arm exertstorque on the side of the flux member 54 from which it projects thatcauses the end of that side of the flux member to move transversely awayfrom the tapered side of the plunger 17. This causes the slope of theinductance-pressure curve to decrease. Once the flux member 54 isdeformed in this manner, the opposite movement of the adjusting screwcauses the slope of the inductance-pressure curve to increase. Thecombination of this torque arm 58 and the axially adjustable member 16allows the entire inductance-pressure curve to be brought withintolerance after manufacture.

It is also desirable, as has been previously mentioned, to provide foran extra boost in fuel supply rate at high manifold absolute pressure byproviding for a similar boost in inductance. In FIG. 5, curves E and Fshow the desired increase in slope in the power enrichment region to theright of the dashed line G. In order to produce such a characteristic,the taper on the nonadjustable gap side of the plunger 17 is made longerand deeper than that on the adjustable gap side of the plunger 17. Inoperation, at low pressures, the adjustable gap is considerably smallerthan the nonadjustable gap and therefore tends to control, since thecontribution of the latter to total inductance is negligible. When thepressure increases to the point where the main taper has completelypassed the adjustable end of the flux member 54, the adjustable gap nolonger decreases with increasing pressure. From this point on, aspressure increases, the non-adjustable gap has an increasing effect uponthe total inductance. The result is a curve such as D, E or F in FIG. 5,depending on the relative sizes of the minimum adjustable andnonadjustable gaps. If the minimum adjustable gap is considerablysmaller than the minimum non-adjustable gap, very little or no powerenrichment boost, such as is shown in curve D, will result. However,higher ratios of minimum adjustable to minimum non-adjustable gap sizeswill produce curves such as E or F, wherein the effect of the variableslope disappears at the highest pressures.

I claim:

1. A variable inductance device comprising, in combination:

an inductive coil with a central axial hole therethrough;

a magnetically permeable plunger axially reciprocable in the hole, oneend of the plunger being tapered on at least one side thereof;

a magnetically permeable flux member fixed to the coil on the outsidethereof, the flux member having a first portion adjacent the tapered endof the plunger and a second portion adjacent the other end of theplunger whereby a magnetic flux path is created through the flux memberand plunger which varies the inductance of the coil with the axialposition of the plunger, the flux member also having a third portion,which third portion comprises a torque arm projecting from the firstportion of the flux member, the torque arm being effective, when biasedin one direction, to deform the flux member so that the first portionmoves transversely with respect to the plunger to further vary theinductance of the coil;

and a member adjustable with respect to the coil, the adjustable memberbeing engageable with the torque arm and effective, when adjusted, tobias the torque arm in the one direction.

2. A variable inductance device comprising, in combination:

an inductive coil with a central axial hole therethrough;

a magnetically permeable plunger axially reciprocable in the hole, oneend of the plunger being asymmetrically tapered on two or more sidesthereof;

a magnetically permeable flux member fixed to the coil on the outsidethereof, the flux member having one portion adjacent each of the taperedsides of the tapered end of the plunger and a further portion adjacentthe other end of the plunger whereby the one end of the plunger has ataper on one side that is both longer and deeper than the taper on theother side.

4. A variable inductance device comprising, in com- 10 bination:

an inductive coil with a central axial hole therethrough;

a magnetically permeable plunger axially reciprocable within the hole,one end of the plunger being asymmetrically tapered on opposing sidesthereof, the taper on one side being longer and deeper than the taper onthe other side;

a magnetically permeable flux member fixed to the coil on the outsidethereof, the flux member having a first portion adjacent the one side ofthe tapered end of the plunger, a second portion adjacent the other sideof the tapered end of the plunger and a third portion adjacent the otherend of the plunger whereby parallel flux paths are created, oneincluding the first portion of the flux member and the other includingthe second portion of the flux member, each of the flux paths beingdominant in determining the rate of change of inductance of the coilover a different range of axial positions of the plunger, the fluxmember also having a fourth portion projecting from the second portionthereof, which fourth portion comprises a torque arm effective, whenbiased in one direction, to deform the flux member so that the secondportion moves transversely with respect to the plunger to further varythe inductance of the coil in the range of axial plunger positions inwhich the second portion is dominant;

and a member adjustable with respect to the coil, the adjustable memberbeing engageable with the torque arm and effective, when adjusted, tobias the torque arm in the one direction.

t s m k

1. A variable inductance device comprising, in combination: an inductivecoil with a central axial hole therethrough; a magnetically permeableplunger axially reciprocable in the hole, one end of the plunger beingtapered on at least one side thereof; a magnetically permeable fluxmember fixed to the coil on the outside thereof, the flux member havinga first portion adjacent the tapered end of the plunger and a secondportion adjacent the other end of the plunger whereby a magnetic fluxpath is created through the flux member and plunger which varies theinductance of the coil with the axial position of the plunger, the fluxmember also having a third portion, which third portion comprises atorque arm projecting from the first portion of the flux member, thetorque aRm being effective, when biased in one direction, to deform theflux member so that the first portion moves transversely with respect tothe plunger to further vary the inductance of the coil; and a memberadjustable with respect to the coil, the adjustable member beingengageable with the torque arm and effective, when adjusted, to bias thetorque arm in the one direction.
 2. A variable inductance devicecomprising, in combination: an inductive coil with a central axial holetherethrough; a magnetically permeable plunger axially reciprocable inthe hole, one end of the plunger being asymmetrically tapered on two ormore sides thereof; a magnetically permeable flux member fixed to thecoil on the outside thereof, the flux member having one portion adjacenteach of the tapered sides of the tapered end of the plunger and afurther portion adjacent the other end of the plunger whereby a pair ofparallel flux paths are created through the plunger and the separateportions of the flux member to vary the inductance of the coil withaxial movement of the plunger.
 3. The variable inductance device ofclaim 2 wherein the one end of the plunger has a taper on one side thatis both longer and deeper than the taper on the other side.
 4. Avariable inductance device comprising, in combination: an inductive coilwith a central axial hole therethrough; a magnetically permeable plungeraxially reciprocable within the hole, one end of the plunger beingasymmetrically tapered on opposing sides thereof, the taper on one sidebeing longer and deeper than the taper on the other side; a magneticallypermeable flux member fixed to the coil on the outside thereof, the fluxmember having a first portion adjacent the one side of the tapered endof the plunger, a second portion adjacent the other side of the taperedend of the plunger and a third portion adjacent the other end of theplunger whereby parallel flux paths are created, one including the firstportion of the flux member and the other including the second portion ofthe flux member, each of the flux paths being dominant in determiningthe rate of change of inductance of the coil over a different range ofaxial positions of the plunger, the flux member also having a fourthportion projecting from the second portion thereof, which fourth portioncomprises a torque arm effective, when biased in one direction, todeform the flux member so that the second portion moves transverselywith respect to the plunger to further vary the inductance of the coilin the range of axial plunger positions in which the second portion isdominant; and a member adjustable with respect to the coil, theadjustable member being engageable with the torque arm and effective,when adjusted, to bias the torque arm in the one direction.